Pros

Pro

Free & Open Source

Pro

Blocks a wide selection of annoying ads

Cons

Con

Users automatically opted in to whitelist

AdBlock+ has an automatic whitelist when installed that allows certain advertisers through the blocking mechanism. The fact that these advertisers pay for this privilege makes this particular scenario rife with conflict of interest.

Con

Uses too much RAM

AdBlock+ tends to use a lot of memory, which has been documented in many use cases as well as admitted by AdBlock themselves. Considering there are alternatives out there that can block ads successfully with half the RAM usage as AdBlock, one has to wonder why this is a problem specific to AdBock.